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Building-wide air delivery conducted through pipes or channels.

Ductless System

A heating and air conditioning system that usually has a wall-mounted indoor unit and an outside compressor. It does not require ductwork.


Used for conducting air to and from an air-handling unit via a pipe or closed conduit made of materials such as sheet metal or fiberglass board.

Downflow Furnace

Draws in return air from the top and expels warm air at the bottom.


A device for recovering superheat from the compressor discharge gas of a heat pump or central air conditioner for use in heating or preheating water.


The reduction of water vapor by cooling the air below the dew point, as well as the removal of water vapor from air by chemical means, refrigeration, etc.

Defrost Cycle

The removal of ice or frost buildup from the outdoor coil during the heating season.


Found in ductwork, this movable plate opens and closes to control airflow and is used in zoning to regulate airflow to certain rooms.